Severed traveling-wave tube with hybrid terminations



April 27, 1965 w. HANT ETAL 3,181,023

SEVERED TRAVELING-WAVE TUBE WITH HYBRID TERMINATIONS l Filed March 29, 1962 5 Sheets-Sheet 1 "y www miwn April 2 7, 1965 w. HANT ETAL SEVERED TRAVELING-WAVE TUBE WITH HYBRID TERMINATIONS 5 Sheets-Sheet 2 Filed March 29, 1962 h I IM\ VIII I IIII I \IIIIIII A. l R\I II I III I, III \I\v v I I @U III I I Il IN I III www //I/II| April 27, 1965 w. HANT ETAL 3,181,023

SEVERED TRAVELING-WAVE TUBE WITH HYBRID TERMINTIONS Filed March 29, 1962 s sheets-sheet s United States Patent O 3,181,023 SEVERE!) 'IRAVELHslG-WAVE E WITH HYBRID TERMINATEONS William Haut and Modrins V. Kreismanis, Los Angeles, Calif., assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Mar. Z9, 1962, Ser. No. 133,439 8 Claims. (Cl. S15- 3.5)

This invention relates generally to traveling-wave tubes, and more particularly relates to a severed traveling-wave tube in which the amplifying sections are terminated by hybrid terminations, i.e., terminations which extend both internally and externally of the slow-wave structure.

In traveling-wave tubes a stream of electrons is caused to interact with a propagating electromagnetic wave in a manner which amplifies the electromagnetic energy. In order to achieve such interaction, the electromagnetic wave is propagated along a slow-Wave structure, such as a conductive helix wound about the path of the electron stream or a folded waveguide type of structure in which a waveguide is effectively Wound back and forth across the path of the electrons. The slow-wave structure provides a path of propagation for the electromagnetic wave which is considerably longer than the axial length of the structure, and hence, the traveling-Wave may be made to effectively propagate at nearly the velocity of the electron steam. The interactions between the electrons in the stream and the traveling-wave cause velocity modulations and bunching of the electrons in the stream. The net result may then be a transfer of energy from the electron beam to the wave traveling along the slow-wave structure, which wave will hereinafter be termed the circuit wave.

The present invention is primarily, although not necessarily, concerned with traveling-wave tubes utilizing slowwave structures of the coupled cavity, or interconnected cell, type. In this type of slow-wave structure a series of interaction cells, or cavities, are disposed adjacent to each other sequentially along the axis of the tube. The electron stream passes through each interaction cell, and electromagnetic coupling is provided between each cell and the electron stream. Each interaction cell is also coupled to an adjacent cell by means of a coupling hole at the end wall delining the cell. Generally, the coupling holes between adjacent cells are alternately disposed on opposite sides of the axis of the tube, although various other arrangements for staggering the coupling holes are possible and have been employed. When the coupling holes are so arranged, a folded waveguide type of energy propagation results, with the circuit wave energy traversing the length of the tube by entering each interaction cell from one side, crossing the electron stream and then leaving the cell from the other side, thus traveling a sinuous, or serpentine, extended path.

In order to ensure stability, high gain traveling-wave tubes have been constructed in several amplifying sections, with a substantially complete sever, or circuit wave isolation, provided between adjacent amplifying sections, and the only coupling between the sections occurring by means of the velocity modulated electron beam. Each amplifying section has a length appropriate for maximum stable gain, and hence it become necessary to terminate each section in a matched load.

One technique which has been used for achieving the necessary termination is to provide terminating elements within lthe slow-wave structure itself. In such arrangements, which are termed internal terminations, one or more attenuating elements, such asV lossy ceramic buttons, are disposed in the slow-wave structure at adjacent ends of the amplifying sections.

The lossy material Y ice Patented Apr. 27, 1965 absorbs circuit wave energy reaching the ends of the sections and thus effectively terminates the sections. However, in traveling-wave tubes which operate with high average power ratings, over wide bandwidths, and throughout large temperature ranges, it is necessary to employ terminating devices more suitable for such operation.

A termination which has been found desirable for high power, wide bandwidth tubes is the external termination. In this type of termination a waveguide is disposed externally of the slow-wave structure and is coupled to the slow-wave structure in the vicinity of the severed end of an amplifying section. An attenuator is disposed in the waveguide for absorbing circuit wave energy coupled into the waveguide from the associated amplifying section, thereby terminating the section.

As high power, wide bandwith traveling-wave tubes are miniaturized, it is obviously desirable to develop terminating devices which are as small, compact and light as possible, While at the same time retaining all the advantages of temperature insensitivity, high power, and wide bandwidth which are achievable with external terminations. Moreover, since in external terminations the same type of waveguide coupling is employed as that used to couple circuit wave energy out of the slow-wave circuit at the output end of the tube, a critical waveguideto-circuit match is necessary for such terminations.

Accordingly, it is a principal object of the present invention to provide improved termination means for a severed traveling wave tube which requires a minimum amount of space and weight and which at the same time facilitates stable operation of the tube over large ambient temperature ranges while maintaining wide bandwidth and high average power rating.

lt is a further object of the present invention to provide a small, compact, Ireliable and inexpensive termination for a high power, severed traveling-wave tube having an improved impedance match with the slow-wave circuit, especially at the edges of the tube passband, and which termination is relatively insensitive to the particular dielectric properties and geometry of the attenuating material used.

It is a still further object of the present invention to provide a high power, wide bandwidth, severed travelingwave tube which is relatively insensitive to changes in ambient temperature and in which the means for terminating the severed sections can be readily integrated into the tube structure so as to provide a .simple and compact device and at the same Vtime maximize the manufacturing e'iciency and minimize the cost of the traveling-wave tube.

It is a still further object of the present invention to provide a terminating device for a high power, wide bandwidth, relatively temperature insensitive, severed traveling-Wave tube in which the need for critically matching a termination-containing waveguide to the slow-Wave circuit is eliminated.

In accordance with the objectives set forth above, the traveling-wave tube of the present invention includes a slow-wave structure for supporting energy exchange between a stream of electrons and circuit wave energy propagated along the slow-wave structure. The slowwave structure is severed into a plurality of amplifying sections and includes means for precluding the passage of circuit wave energy between adjacent amplifying sections while permitting the passage of the electron stream -between the sections. The slow-wave structure also includes termination cavities which are located adjacent the precluding means at the severed ends of the adjacent amplifying sections. The termination cavities extend beyond the remainder of the slow-wave structure in a direction essentially perpendicular to the path of the elecron stream. An attenuating element, which extends both internally and externally of the said remainder of the slow-wave structure, is disposed in each termination cavity for absorbing circuit Wave energy, thereby terminating the associated amplifying section.

Other and further objects, advantages, and characteristic features of the present invention will become readily apparent from the following detailed description of preferred embodiments of theV invention when taken in conjunction with the appended drawings in which:

FIG. 1 is an over-al1 view partly inlongitudinal section and partly broken away of a traveling-wave tube constructed in accordance with the present invention;

FIG. 2 .is a longitudinal sectional view of a portion of the tube illustrated in FIG. 1 which includes an isolation section;

FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 2; Y

FIG. 4 is a cross-sectional view similar to FlG. 3 illustrating a slightly modied termination;

FIG. 5 is a longitudinal sectional view of a portion of a traveling-wave tube, including an isolation section, constructed according to another embodiment of the present invention;

FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5; and

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 5.

Referring now to the drawings, and more particularly to FIG. 1, the reference numeral 10 designates generally a traveling-wave tube which includes an arrangement 12 Vof magnets, pole pieces and spacer elements which will be described in detail later. with respect to FIG. 2. At this point it should sutiice to statethat the spacer elements and interior portions of the Ypole pieces function as a slowwave structure, while the magnetsV and pole pieces constitute a periodic focusing device for the electron beam traversing the length of the slow-wave structure.

Coupled to the input end of the arrangement 12 is an input waveguide transducer 14 which includes an irnpedance step transformer 16. A ilange 18 is provided for coupling the assembled traveling-wave tube 10 to an external waveguide or other microwave transmission line (not shown). The construction of the flange 18 may include a microwave window (not shown) transparent to microwave energy but capable of maintaining a vacuum within the traveling-wave tube 10. At the output end of the arrangement 12 an output transducer 20 is provided which is substantially similar to the input transducer 14 and which includes an impedance step transformer 22 and a coupling flange 24, which elements are similar to the elements 16 and 18, respectively, of the input transducer 14. For vacuum pumping or out-gassing the traveling-wave tube 10 during manufacture, a double- V backward Wave device is desired. The electron gun 28- functions to project a stream of electrons along the axis of the tube 10 and may be of any conventional construction well known in the art. For details as to the construction of the gun 28 reference is made toPatent No.

2,985,791, entitled Periodically Focused Severed Traveling-Wave Tube, issued May 23, 1961, to D. J. Bates et al., and assigned to the assignee of the present invention, and to Patent No. 2,936,393, entitled Low Noise Traveling- Wave Tube, issued May 10, 1960, to M. R. Currie et al., and assigned to the assignee of the present invention.

At the output end of the traveling-wave tube 16 there is provided a cooled collector structure 3) for collecting the electrons in the stream. The collector is conventional and may be of any form well known in the art. For details as to the construction of the collector, reference is made to the aforesaid Patent No. 2,985,791 and to Patent 4 No. 2,860,277, entitled Traveing-Wave Tube Collector Electrode, issued November ll, 1958, to A. H. Iversen, and assigned to the assignee of the present invention.

The construction of the slow-wave structure, focusing system, and terminations of the traveling-wave tube 10 are illustrated in more detail in FIG. 2. A plurality of essentially annular disk-shaped focusing magnets 32 are interposed between a plurality of ferromagnetic pole pieces 34. As illustrated in FIG; 3, the magnets 32 may be diametrically split into` two sections32a and 32b for convenience during assembly of the tube. The ferromagnetic pole pieces 34 extend radially inwardly of the magnets 32 to approximately the perimeter of the region adapted to contain the -axial electron stream; The individual lpole pieces are constructed in such a manner that a shont drift tube, or ferrule, 36 is provided at the inner extremity of each pole piece. The drift tube 36 is in the form of a cylindrical extension, vor lip, protruding axially along the path of the electron stream from both surfaces of pole piece 34, i.e., in both directions normal to the plane of the pole piece 34. The drift tubes 36 are provided with central and axially aligned apertures 38 to provide a passage for the dow of the electron beam. Adjacent ones of the drift tubes 36 .are separated by a gap 40 Awhich functions as a magnetic gap to provide a focusing lens rfor the electron beam and also as an interaction gap in which energy exchange between the electron beam and circuit wave energy traversing the slow-wave structure occurs.

Disposed radially within each of the magnets 32 is an annular slow-wave circuit spacer element 42 of a conductive non-magnetic material such as copper. Each spacer element has a central cylindrical aperture 44 to provide space for a microwave interaction cell, or cavity, 46 which is defined by the inner lateral surface of the spacer 42 and the walls of the two adjacent pole pieces 34 projecting inwardly of the spacer element 42. The inner diameter of the spacer 42 determines the radial extent of .the inter action cell 46, while the axial length of the spacer 42 determines the axial length of the cell 46.

For interconnecting adjacent interaction cavities 46 an off-center coupling hole 48 is provided through each of the pole pieces 34 to Ipermit the transfer of circuit wave energy from cell to cell. As is illustrated, the coupling holes 48 may be substantialy kidney-shaped and may be alternately disposed apart with respect to the drift tubes 36. I-t should be pointed out, however, that the coupling holes 48 may be of other shapes and may be staggered in various other arrangements, such as those disclosed in Patent No. 3,010,047, entitled Traveling- Wave Tube, issued November 21, 1961, to D. I. Bates, and assigned tothe assignee of the present invention. In

any event, it will be apparent that the spacer elements 42 and the portions of the pole pieces 34 projecting inwardly of the spaces 42 not only form an envelope for the tube, but also constitute a slow-wave structure -for propagating circuit wave energy in a serpentine path along the axially traveling electron stream so as to support energy exchange between the electrons of the stream and the circuit wave.

The axial length of the magnets 32, hence that of the spacers 42, is equal to the spacing between adjacent pole pieces 34, and the radial extent of the magnets 32 is approximately equal to or, as shown, slightly greater than that off the pole pieces 34. To provide focusing lenses in the gaps 40, the magnets 32 are stackedwith alternating polarity along the axis of the tube, thus causing a reversal of the magnetic eld at each magnetic lens and thereby providing a periodic focusing device. It should be pointed out, however, that although the lengths of the spacers 42 may be substantially constant, they rnay also be varied slightly with respect to each other so that the effective axial length of the cavities 46 lis varied as a function of distance along the tube to ensure thatthe desired interaction between the electron stream and the traveling waves will continue to a maximum degree even though the electrons are decelerated toward the collector end of 5 the tube. For such arrangements reference is made to Patent No. 2,956,200, entitled Periodically Focused Traveling-Wave Tube With Tapered Phase Velocity, issued October 11, 1960, t'o D. l. Bates, and assigned to the assignee of the present invention.

As has been pointed out above, in order to ensure stabili-ty and freedom from oscillations on account of possible regenerative feedback, high gain traveling-wave tubes of the type with which the present invention is concerned may be constructed in several amplifying sections. Thus, in FIG. l, the traveling-wave tube I is illustrated as having three amplifying sections 52, 54 and 55, although it is to be understood that three such sections are shown solely for illustrative purposes. Each of the amplifying sections is isolated from adjacent `sections by means of an isolator section. Thus, in the thaveling-wave tube of FIG. 1, the first and second amplifying sections 52 and 54, respectively, are isolated from each other by isolator section 58; while the second and third amplifying sections 54 and 56, respectively, .are isolated from one another by means off isolator section 60. The isolator sections 58 and 60 provide a substantially complete sever, or isolation for circuit wave energy, between adjacent amplifying sections of the traveling-Wave tube 10, while at the same time allowing the electron stream to pass through the entire length of the traveling-wave tube. The electron stream is modulated in each amplifying section, and hence as it enters the subsequent amplifying section it launches a new circuit wave therein which is amplified by interaction between the new circuit wave and the electron stream. Thus, unidirectional coupling between adjacent amplifying sections is provided through the electron stream.

The isolator section 58 is illustrated in more detail in FIGS. 2 and 3, it being understood that isolator section 60 is .constructed in ain identical manner. Isolator section 58 is formed in a substantial continuity of the pole piece-magnet-spacer assembly 12. However, in the isolator section modified pole pieces 31, 33 and 35 are used. The pole pieces 31 and 33, which are located at the axial extremities of the isolator section 58, 'are identical to the pole pieces 34 ordinarily used in the remainder of the tuberexcept that the respective coulpling holes 41 and 43 in the pole pieces 31 and 33 are smaller than the normal coupling holes 48. The pole piece 35 axially located in the center of the isolator section S differs from the remaining pole pieces in that no`coupling hole for circuit wave energy is provided in the pole piece 35. This prevents circuit wave energy in .amplifying section 52 from passing into the section 54, and vice Versa, thereby achieving circuit wave isolation between the sections 52 and 54.

A rectangular ring-like member 62, of a conductive non-magnetic material such as copper, is disposed between pole pieces 31 and 35 in lieu of a spacer element 42, and an identical rectangular ring-like member 64 is located between the pole pieces 33 and 35. The members 62 and 64, together with the adjacent pole pieces, define elongated rectangular termination cavities 45 and 47, respectively. The cavities 45 and 47 are eccentrically located with respect to the drift tubes 36, each extending in a direction perpendicular to the axis of the tube from slightly beyond the reduced size coupling hole 41 or 43 on one side of the axis of the tube to almost the outer extremity of the pole pieces on the opposite side of the axis of the tube. As is shown in FIG. 2, the cavity 45 exists substantially on one side of-the drift tubes 36, while the cavity 47 exists substantially on the opposite side of the drift tubes, although this is not essential for satisfactory operation. Obviously, the magnet sections 32a and 3217 which are disposed between the pole pieces Y in the isolator section 58 have recessed portions to conform to the shape of the cavity-defining members 62 and 64. Although the axial length of the termination cavities 45 and 47 is illustrated as being the same as that of the remaining interaction cavities, it may also be greater or smaller than the axial length of the remaining cavities.

Elements 74 and 80 of attenuating material are disposed within the elongated rectangular termination cavities 4and 47, respectively, to dissipate circuit wave energy entering these cavities with essentially no reflection back into the respective amplifying sections 52 and 54. The attenuators 74 and 80 may be of lossy ceramic material, for example a mixture of forsterite and silicon carbide, with the percentage of silicon carbide varying from essentially to essentially 80%. Examples of other materials which could beV used are silicon carbide and alumina, silicon carbide and talc, silicon carbide and beryllia, or other lossy material and ceramic combinations. As is shown in FIGS. 2 and 3, the attenuator 74 is in a form of a wedge-shaped element, with the narrow edge of the wedge being located adjacent the drift tube 36 and the wedge taper being such that the element 74 contacts the pole piece 35 slightly inwardly of the remote end of the cavity 45, leaving a portion 76 of the lateral surface of the element 74 parallel to and in contact uu'th pole piece 35. The attenuator 80 is, of course, identical to the attenuator 74. 'I'he particular dimensions of the attenuators 74 and 80 are determined by the dielectric constant e and the loss constant e" of the lossy material used and the particular frequencies of circuit wave energy to be attenuated. The minimum length of the attenuators is selected according to the condition that the circuit wave energy be substantially absorbed when it reaches the end of the attenuator remote from the drift tube 36.

It should be pointed out that the wedge-shaped attenuating elements illustrated in FIGS. 2 and 3 simply represent one manner of achieving the necessary dissipation of circuit wave energy, and alternate forms of attenuators may be employed without departing from the principles of the invention. For example, the attenuating element may have the shape of a rectangular parallelepiped, a stepped element of rectangular cross-section, a pyramid, or a multiple wedge-shaped element.

One slightly modified form of hybrid termination is illustrated in FIG. 4. In this modification the elongated termination cavities are not completely rectangular, but rather a ring-like cavity-denning member 92 is employed which has inwardly extending oblique portions 93 and 95 adjacent its end remote from the drift tube 36. The lossy attenuating element 94 disposed within the ring-like member 92 is, of course, appropriately shaped to fit within the modified termination cavity defined by the member 92. This type of termination permits more mag netic material to surround the termination cavities.

In the operation of the traveling-wave tube 10, circuit wave energy of microwave frequencies traverses the slowwave structure from the electron gun end to the collector end, being amplified first in section 52 due to its'interaction with the electron stream. Near the output of this amplifying section, the circuit wave has grown and has caused considerable charge density modulation in the electron stream. The circuit wave in the section 52 traveling toward the section 54 enters the elongated cavity 45 in the isolator section 53 through coupling hole 41. Since there is no circuit wave coupling hole in the pole piece 35, this wave is precluded from entering the next amplifying section 54 and is substantially dissipated in the attenuating element 74. Nevertheless, the modulated electron stream passes'through isolator section 58 and into amplifying section 54, launching a new circuit wave in section 54. The new circuit wave is amplified by interaction with the electron stream until reaching isolator section 60. Moreover, circuit wave energy in section 54 which is traveling toward the section 52 will enter the elongated cavity 47 in isolator section 58 through the coupling hole 43, being substantially absorbed in lossy attenuating element 80. The isolator section functions in the same manner as the section 58 to dissipate circuit wave energy from the section 54 which has traveled toward the collector, as well as circuit wave energy from the section 56 which has traveled toward the electron gun. Again, the modulated electron beam passes through the isolator section 60 and launches a new circuit wave in section 56. This new Wave is amplified by interaction with the electron stream in the section 56, and the amplitied output wave is fed from the section S to output waveguide transducer 22.

The terminations heretofore described are especially suitable for use in a traveling-wave tube having a permanent magnet periodic focusing system. However, the principles of the present invention are in no way limited to periodically focused tubes but may also be employed .in tubes using other types of focusing schemes, such as solenoid focusing or non-periodic permanent magnet focusing. One manner in which the hybrid terminations of the present invention may be used in a solenoid-focused traveling-Wave tube is illustrated in FIGS. 5-7.

The slow-wave structure of the embodiment of FIGS. 5-7 comprises a series of alternating spacer elements 142 @and transverse vanes 134. The elements 142 and vanes 134 are .similar to the spacers 42 and the inner portions of the pole pieces 34, respectively, of the embodiment of FIG. 2, except that both the spacers 142 and the vanes 134 may be of a conductive non-magnetic material such as copper. circuit spacer 142 is cylindrical, while the outer surface of each spacer 142 includes a pair Yof oppositely disposed at portions 135 Yand 137 of rectangular cross-section. Each transverse vane 134, the outer surfaces of which are shaped the same as the outer surfaces of the spacers 142, defines a drift tube, or ferrule, 1,36 in its central region, which .drift tubes are `identical with the drift tubes 36 of FIG. 2.' The vanes 134 and spacer elements 142 delline a series of interaction cavities 146 which are intercoupled through coupling holes 1418 in the vanes 134.

The inner surface 144 of each slow-wave An interaction gap 140 is provided between each pair of adjacent drift tubes 1:36.

The electron stream traversing the drift tubes 136 via apertures 138 is focused by means of a solenoid 13-2 which is concen-trically disposed about and longitudinally coextensive with the arrangement of spacers 142 and vanes 134. The inner surface of the solenoid 132 lies.

adjacent the cylindrical portions of the outer surfaces orf the spacer elements 142 andthe vanes 134. The space between the solenoid 132 and the flat portions of the outer surfaces of the spacer elements 142 and the vanes 134 along one side of the spacer-vane assembly is used to accommodate a waveguide 1117. The waveguide 117 supports the propagation of electromagnetic wave energy into or out of the slow-wave structure.

'Ilhe isolator section for the embodimen-t of FIGS. 5-7 employs Vthree special, or slightly modified, transverse vane members 104, 114, and 124 instead of the vanes 134 ordinarily used in the remainder of the tube. The vane members 104 and 114 differ from the vane members 134 in that the vane mem-bers 104 and 114 define portions 106 and 116, respectively, which project beyond the extremity of the ordinary vanes 134 and spacers 142 into the space between the solenoid 132 and the flat portions of the outer surfaces ofthe spacer elements 142 andthe vanes 134 on the Side of .the assembly opposite from the. waveguide 11.7. Also, the coupling holes 141 and 143`in the vanes 104 and 1.14, respectively, are smaller than the coupling holes 148 in the vanes 134. The transverse vane 124, which is axially located in the center of the isolator section, is identical to the vanes 164 and 114 except no coupling hole for circuit wave energy is provided in the vane 124. This prevents circuit Wave energy from passing between amplifying sections 152 and 154, thereby achieving circuit wave isolation between the sections 152 and 154.

A modified, or termination, spacer element 162, which may be of a conduct-ive non-magnetic material such as copper, is disposed between the vanes 104 and 124. The

spacer 162 has an outer shape identical to the outer shape of vane members 104, 114 and 1-24 and denes an essentially rectangular aperture 167. The aperture 167 extends from slight-ly beyond the coupling hole 141 on one side of the axis of thetube to well beyond the surfaces 137 of ordinary spacers 142 on the opposite side of the axis of the tube. Moreover, the aperture 167 has inward- 4ly projecting oblique surfaces 163 and 165 adjacent its end more remote from the coupling hole 141. A termination spacer 164 identical to the spacer 162, and having an aperture 1161, is disposed between the vane members 114 and 124 in the isolator section. The spacer 162, together with the vane members 104 and 124 denes an elongated essentially rectangular cavity 145, while the spacer 164, together with vane members 1'14 and 1124 denes a like cavity 147.

YA lossy attenuating element 174, which may be of the materials se-t forth above for attenuators 74 and 80 of FIG. 2, is disposed in the elongated termination cavity 145, and a similar attenuator .180 is located in the cavity 147. As is illustrated in FIGS. 5-7, the attenuators 174 and 180 are in the form of wedge-shaped elements, with the narrow edge of the wedge being located adjacent the drift tube 136 and the wedge taper being such that the wedge contacts the vane 124 slight-ly inwardly of the end of the cavity remote from the drift tube 136. Alternately, the attenuators 174 and 160 may be of the various other shapes described above with reference to the attenuating elements 74 and 80 of FIG. 2.

The operation of the terminating means of FIGS. 5-7 issirnilar to that of the terminations of FIGS. 2 and 3. Circuit wave energy traversing amplifying section 152 of the slow-wave structure in the direction of section 154 enters termination cavity via coupling hole1-41 and is substantially dissipated in attenuator 174.` Circuit wave energy in section 154 traveling tow-ard section 152 is coupled into termination cavity 147 through aperture 143, this energy being dissipated in attenuator 180. The transverse vane member 124, of course, prevents circuit Wave energy from passing between amplifying sections 152 and 154, although the electron stream is allowed to pass through the vane 124 via the aperture in the drift tube thereof.

The hybrid terminating devices disclosed herein are able to attenuate substantially all of the large amounts of circuit wave energy present at adjacent ends of the amplifying sections in a high power, severed travelingwave tube. The arrangement achieves proper attenuation of the circuit wave energy throughout a great range of temperatures, while maintaining highY power, wide bandwidth operation. In addition, .the terminations are readily integratable into the tube structure, thereby providing a simple and compact device which achieves the desired large amount of attenuation without increasing the radial extent of the tube over that of a corresponding tube having no terminations.

Although the present invention has been Yshown and described with reference to specific embodiments, nevertheless, various changes and modifications obvious to one skilled in the art are deemed to be within the spirit, scope and contemplation in the invention as set forth in the appended claims.-

Wha-t is claimed is:

1. A traveling-wave tube of the type which is severed into a plurality of amplifying sections, each isolated from one another with respect to circuit wave energy comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(b) a wave propagating structure disposed along and about said path for propagating circuit Wave energy in such manner that it interacts with said stream of electrons;

(c) means disposed between each pair of adjacent amplifying sections for precluding the passage of circuit wave energy between said adjacent amplifying sections while permitting the passage of said stream of electrons therebetween;

(d) said wave propagating structure including at least one termination cavity deiining member disposed adjacent said precluding means;

(e) the cavity deiined by said member extending beyond the remainder of said wave propagating structure in a direction essentially perpendicular to said predetermined path of said stream of electrons; and

(f) loss ,means disposed in said cavity for attenuating circuit wave energy;

(g) said loss means extending internally and externally of said remainder of said wave propagating structure along said perpendicular direction.

2. A traveling-wave tube comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of iixed length;

(b) a wave propagating structure divided into at least first and second amplifying sections and disposed along and about said path for propagating circuit wave energy in such manner that it interacts with said stream of electrons;

(c) means for precluding the passage of circuit wave energy between said first and second amplifying sections while permitting the passage of said stream of electrons therebetween;

(d) said wave propagating structure including a iirst termination cavity deiining member disposed adjacent said precluding means on the side of said irst amplifying section and a second termination cavity defining member disposed adjacent said precluding` means on the side of said second amplifying section; (e) the cavity dened by said iirst member extending eyond the remainder of said wave propagating structure in a direction essentially perpendicular to said predetermined path of said stream of electrons;

(f) the cavity detined by said second member extending beyond the remainder of said wave propagating structure in a direction essentially perpendicular to said predetermined path of said stream of electrons; and

(g) loss means disposed in each of the said cavities for attenuating circuit wave energy;

(h) said loss means extending internally and externally of said remainder of said wave propagating structure along said perpendicular direction.

3. A traveling-wave tube comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(b) a plurality of groups of intercoupled cavities disposed sequentially along and about said path for propagating circuit wave energy and providing energy exchange between said electron stream and said circuit wave energy;

(c) means disposed between adjacent end cavities in adjacent ones of said groups for precluding the passage of circuit wave energy between said adjacent end cavities while permitting the passage of said stream of electrons therebetween;

(d) said end cavities extending beyond the remainder of said interaction cavities in a irst radial direction and terminating inwardly of said remainder of said interaction cavities in a radial direction opposite to said iirst radial direction; and

(e) loss means disposed in each said end cavity for attenuating circuit Wave energy;

(f) said loss means extending internally and externally of said remainder of said interaction cavities along said lirst radial direction.

4. A traveling-wave tube according to claim 3 wherein said loss means comprises an element of lossy ceramic material, said element having a smaller cross-sectional area Y at its end nearer the region adapted to contain said stream of electrons than at its end farther from said electron stream region.

5. A traveling-wave tube according to claim 4 wherein said element is substantially wedge-shaped, with the narrow end of said element being located slightly externally of the region adapted to contain said stream of electrons and the wide end of said element being located adjacent the end of said end cavity farthest from said electron stream region. v

6. A traveling-wave tube according to claim 3 wherein the cross-section of each of said end cavities in a plane perpendicular to said predetermined path of said electron stream is essentially rectangular and the cross-section of each of said remainder of said interaction cavities in a plane perpendicular to said predetermined path is circular.

7. A traveling-wave tube comprising:

(a) collector means;

(b) electron gun means for emitting a stream of electrons;

(c) a plurality of axially aligned apertured magnets of alternating polarity and a plurality of ferromagnetic pole pieces interposed between and abutting adjacent ones of said magnets for producing a periodic magnetic focusing field for constraining said stream of electrons to flow along a predetermined path toward said collector means;

(d) a non-magnetic apertured spacer element disposed within each of said magnets and having an outer perimeter essentially equal to the inner perimeter of the associated magnet;

' (e) said pole pieces projecting internally of the apertures in said spacer elements to deiine therewith a plurality of groups of intercoupled interaction cavities arranged sequentially along and in electromagnetic interacting relationship with said stream of electrons;

(f) means disposed between adjacent end cavities in adjacent ones of said groups for precluding the passage of circuit wave energy between said adjacent end cavities while permitting the passage of said stream of electrons therebetween;

(g) said end cavities extending beyond the remainder of said interaction cavities on one side of the region adapted to contain said stream of electrons and terminating inwardly of said remainder of said interaction cavities on the opposite side of said electron stream region; and

(h) loss means disposed in each said end cavity for attenuating circuit wave energy;

(i) said loss means extending internally and externally of said remainder of said interaction cavities on said one side of said electron `stream region.

8. A traveling-wave tube comprising:

(a) collector means;

(b) electron gun means for emitting a stream of electrons;

(c) a solenoid for producing an axial magnetic iield constraining said stream of electrons to ow along a predetermined path toward said collector means;

(d) slow-wave structure means for propagating circuit wave energy disposed within said solenoid and between said electron gun means and said collector means;

(e) said slow-wave structure means comprising a plurality of axially aligned apertured spacer elements and a plurality of Vane members interposed between and projecting internally of the apertures in said spacer elements, sa-id spacer elements and vane members defining a plurality of groups of intercoupled interaction cavities arranged sequentially along and in electromagnetic interacting relationship with said stream of electrons;

(f) means disposed between adjacent end cavities in adjacent ones of said groups for precluding the passage of circuit wave energy between said adjacent 1 1 end cavities while permitting the passage `of said stream of electrons therebetween;

(g) said end cavities extending beyond the remainder of said interaction cavities on one side of the region adapted to contain said stream of electrons and terminating inwardly of said remainder of said interaction cavitieson the opposite side of said electron stream region; and

(h) loss means disposed in each said end cavity for attenuating circuit wave energy;

(i) said loss means extending internally and externally of said remainder of said interaction cavities on said one side of said electron stream region.

References Cited by the Examiner UNITED STATES PATENTS 2,939,993 6/60 Zublin et al 315-35 2,967,968 1/61 Nalos S15-3.5 2,985,792 5/61 Bates et al S15- 3.5

GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner. 

8. A TRAVELING-WAVE TUBE COMPRISING: (A) COLLECTOR MEANS; (B) ELECTRON GUN MEANS FOR EMITTING A STREAM OF ELECTRONS; (C) A SOLENOID FOR PRODUCING AN AXIAL MAGNETIC FIELD CONSTRAINING SAID STREAM OF ELECTRON TO FLOW ALONG A PREDETERMINED PATH TOWARD SAID COLLECTOR MEANS; (D) SLOW-WAVE STRUCTURE MEANS FOR PROPAGATING CIRCUIT WAVE ENERGY DISPOSED WITHIN SAID SOLENOID AND BETWEEN SAID ELECTRON GUN MEANS AND SAID COLLECTOR MEANS; (E) SAID SLOW-WAVE STRUCTURE MEANS COMPRISING A PLURALITY OF AXIALLY ALIGNED APERTURED SPACER ELEMENTS AND A PLURALITY OF VANE MEMBERS INTERPOSED BETWEEN AND PROJECTING INTERNALLY OF THE APERTURES IN SAID SPACEER ELEMENTS, SAID SPACER ELEMENTS AND VANE MEMBERS DEFINING A PLURALITY OF GROUPS OF INTERCOUPLED INERACTION CAVITIES ARRANGED SEQUENTIALLY ALONG AND IN ELECTROMAGNETIC INTERACTING RELATIONSHIP WITH SAID STREAM OF ELECTRONS; (F) MEANS DISPOSED BETWEEN ADJACENT END CAVITIES IN ADJACENT ONES OF SAID GROUPS FOR PRECLUDING THE PASSAGE OF CIRCUIT WAVE ENERGY BETWEEN SAID ADJACENT END CAVITIES WHILE PERMITTING THE PASSAGE OF SAID STREAM OF ELECTRONS THEREBETWEEN; (G) SAID END CAVITIES EXTENDING BEYOND THE REMAINDER OF SAID INTERACTION CAVITIES ON ONE SIDE OF THE REGION ADAPTED TO CONTAIN SAID STREAM OF ELECTRONS AND TERMINATING INWARDLY OF SAID REMAINDER OF SAID INTERACTION CAVITIES ON THE OPOSITE SIDE OF SAID ELECTRON STREAM REGION; AND (H) LOSS MEANS DISPOSED IN EACH SAID END CAVITY FOR ATTENUATING CIRCUIT WAVE ENERGY; (J) SAID LOSS MEANS EXTENDING INTERNALLY AND EXTERNALLY OF SAID REMAINDER OF SAID INTERACTION CAVITIES ON SAID ONE SIDE OF SAID ELECTRON STREAM REGION. 